The present invention relates to magneto-optical and other optical disks where a stable tracking control is effected by means of restraint of crosstalk which may occur in the information pre-recorded in the form of pit strings and changes in the track width, and also relates to recording/reproducing devices intended for use with these disks.
Magneto-optical disks as rewritable optical recording media are already have been already developed from magneto-optical recording media and put into practical use. Stored data is deleted on these kinds of magneto-optical disks by a semiconductor laser emitting a light beam which is focused on the optical recording media to locally elevate the temperature of the magneto-optical recording media. To reproduce recorded data, a light beam is focused on the magneto-optical recording media with such an intensity that the data is not deleted, and the polarization of the reflected light is checked. To reproduce address information on these magneto-optical recording media, continuous pit strings are typically provided in advance in a recording track to form a spiral line or concentric lines on the disk substrate, and the quantity of reflected light is measured for changes which result from the provision of the pit strings.
Meanwhile, super-resolution magnetic reproduction has been developed based on a multilayered magnetic film. In addition, the reproduction resolution of super-resolution magneto-optical recording media has improved a lot. These are contributing factors in the great effort put in those researches about land and groove recording schemes whereby data is recorded and reproduced both in the groove region serving as a guide groove and in the land region serving as another guide groove. In the land and groove recording scheme, the land and the groove constitute individual recording tracks, and require separate sets of address bits.
Now reference is made to FIG. 20 which illustrates a structure of address bits disclosed in Japanese Laid-Open Patent Application No. 7-153081/1995 (Tokukaihei 7-153081 published on Jun. 16, 1995; hereinafter, xe2x80x9cLaid-Open Patent Application 1xe2x80x9d). Grooves (G1, G2) and lands (L1, L2) are provided to form spiral lines with a substantially identical width. A first pit string P1 representing first address information is provided following the groove G1, to form convexities and concavities in a first address region. A second pit string P2 is provided following the groove G2 in a second address region that is displaced along the length of the track off the first address region where the first pit string P1 is provided.
Now, the following will discuss how to reproduce the address information. In a case when a light beam spot BG1 scans the groove G1 relatively as a result of the rotation of the optical disk, the address information of the groove G1 is reproduced by detecting the quantity of reflected light which varies when the light beam spot BG1 scans the first pit string P1 in the first address region. The light beam spot BG1 then passes over the second address region. In a case when a light beam spot BG2 scans the groove G2 relatively, the address information of the groove G2 is reproduced by detecting the quantity of reflected light which varies when the light beam spot BG2 first passes over the first address region and then scans the second pit string P2 in the second address region.
In contrast, in a case when a light beam spot BL1 scans the land L1 relatively, the address information of the land L1 is reproduced by detecting signals which leak from the first pit string P1 and which changes the quantity of reflected light when the light beam spot BL1 scans near the first pit string P1 in the first address region. In a case when a light beam spot BL2 scans the land L2 relatively, the address information of the land L2 reproduced by detecting signals which leak from the second pit string P2 and which changes the quantity of reflected light when the light beam spot BL2 scans near the second pit string P2 in the second address region. This way, an optical disk is made such that address information can be reproduced both in the land and in the groove.
Now reference is made to FIG. 21 which illustrates a structure of addresses disclosed in Japanese Laid-Open Patent Application No. 9-17033/1997 (Tokukaihei 9-17033 published on Jan. 17, 1997; hereinafter, xe2x80x9cLaid-Open Patent Application 2xe2x80x9d). Grooves (G1, G2) and lands (L1, L2) are provided to form spiral lines with a substantially identical width. A first pit string P1 representing first address information is provided following the groove G1 in a first address region. A second pit string P2 is provided following the groove G2 in a second address region that is displaced off the first address region along the length of the track. The width of the groove is widened partially in radial directions to form pits p1 and p2 in the first and second pit strings P1 and P2.
The address information is reproduced, similarly to Laid-Open Patent Application 1, through changes in the quantity of reflected light in the address regions in the land and in the groove. This way, an optical disk is made such that address information can be reproduced both in the land and in the groove.
Now reference is made to FIG. 22 which illustrates a structure of addresses disclosed in Laid-open Patent Application 2. Grooves (G1, G2) and lands (L1, L2) are provided to form spiral lines with a substantially identical width. A wobbling groove representing address information is provided following the groove G1 in a first address region. Another wobbling groove representing address information is provided following the groove G2 in a second address region displaced off the first address region along the length of the track.
The address information is reproduced and detected, similarly to Laid-Open Patent Application 1, by means of the wobbling grooves causing changes in the quantity of reflected light in the address regions in the land and in the groove. This way, an optical disk is made such that address information can be reproduced both in the land and in the groove. Alternatively, the address information is reproduced and detected by means of the wobbling grooves in the address regions caused changes in push-pull signals.
Laid-Open Patent Application 1, however, admits in the description that tracking is unstable. We now discuss this problem in the following.
FIG. 23 is an enlarged view of the first address region of FIG. 20. Symmetric push-pull signals are obtained from the light beam spot BG1 scanning the groove G1, and tracking is effected such that the first pit string P1 is always located in the center of the light beam spot BG1, because the first pit string P1 cuts through the center of the light beam spot BG1.
In contrast, since the pit string P1 is located to the left of the light beam spot BL1 (or closer to the circumference of the disk, for example) in the first address region in the figure, asymmetric push-pull signals are obtained from the light beam spot BL1 scanning the land L1 where there is a gap between pits p1 which are located next to each other along the length of the track. As a result, the light beam spot BL1 moves left as shown in the figure (closer to the pit string P1) while tracking, which renders the tracking unstable. In a worst scenario, the light beam spot BL1 jumps to a different track when moving in the address region. Therefore, in some devices for recording/reproducing such optical disks, a tracking control is temporarily suspended in the address region.
Laid-Open Patent Application 2 also admits in the description that tracking is unstable. FIG. 24 is an enlarged view of the first address region in FIG. 21. The formation of the first pit string P1 constituted by pits p1 that are wider than the groove in the first address region makes push-pull signals obtained from the light beam spot BG1 scanning the land L1 asymmetric as shown in the figure. As a result, the light beam spot BL1 moves right as shown in the figure (closer to the groove G21) while tracking, which renders the tracking unstable. In a worst scenario, the light beam spot BL1 jumps to a different track when moving in the address region. Therefore, in some devices for recording/reproducing such optical disks, a tracking control is temporarily suspended in the address region.
As to the second structure of FIG. 22 disclosed in Laid-Open Patent Application 1, the address is given in the form of wobbling grooves. Push-pull signals become asymmetric for sure, but the wobbling of the groove makes it possible for the light beam spot to be located substantially at the center of the wobbling groove. This way, stable tracking is effected. There is however a setback to the structure. The wobbling groove is formed to continuously bend rightward and leftward; as a result, reproduced and detected signals slowly change reflecting the continuous wobbling. The reproduction signals, representing the address information, show poor quality.
The present invention is intended to solve these problems, and has objectives to offer magneto-optical and other optical disks where a stable tracking control is effected by means of restraint of crosstalk which may occur in the information pre-recorded in the form of pit strings and changes in the track width, and also relates to recording/reproducing devices intended for use with these disks.
An optical disk in accordance with the present invention utilizes both a groove and a land as a recording track and includes:
a first pit string of pits lined along a length of a track, provided in a first recording track which is either a groove or a land; and
a second pit string of pits lined along a length of a track, provided in a first recording track which is adjacent, in a radial direction of the disk, to the first recording track in which the first pit string is provided,
wherein:
the second pit string is displaced off the first pit string along a length of a track so as not to overlap the first pit string in a radial direction of the disk; and
an interval between two pits which are adjacent along a length of a track in the first and second pit strings is specified to be equal to, or less than, half a width of the two pits measured in a radial direction of the disk.
In the conventional technology disclosed in Laid-Open Patent Application 1, pits are located discretely so that addresses are stored by the intervals between pits and the lengths of pits. Some intervals are therefore greater than others, which causes asymmetric push-pull signals to be produced when a light beam spot moves over an address region in a recording track which is a land. This undesirably destabilizes tracking.
In contrast, in the optical disk in accordance with the present invention, the interval between two pits which are adjacent along the length of the track in the first and second pit strings is specified to be equal to, or less than, half the width of the two pits measured in a radial direction of the disk. Therefore, the tracking signal is hardly disturbed (or disturbed for a very short time) by the gaps in the pit strings. This arrangement effects more stable tracking compared with the preceding optical disk in which pits are located discretely. Further, the pit strings which are adjacent in a radial direction of the disk (i.e., the first pit string P1 and the second pit string P2) are provided displaced along a length of a track and do not overlap each other in a radial direction of the disk. Therefore, when the land or the groove is scanned, signals reproduced from the first pit string P1 and those from the second pit string P2 are clearly separated and can be read accurately.
An optical disk in accordance with the present invention utilizes both a groove and a land as a recording track and includes:
a first width varying portion, having a track width which varies between a first width and a second width, provided in a first recording track which is either a groove or a land; and
a second width varying portion, having a track width which varies between a first width and a second width, provided in a first recording track which is adjacent, in a radial direction of the disk, to the first recording track in which the first width varying portion is provided,
wherein:
the second width varying portion is displaced off the first width varying portion along a length of a track so as not to overlap the first width varying portion in a radial direction of the disk; and
WG≈WL and W1 less than WG less than W2, where WG is a width of the groove, WL is a width of the land, W1 is the first width, and W2 is the second width.
In Laid-Open Patent Application 2, the width in the address region is greater than the width of the groove. Therefore, push-pull signals are asymmetric in the land, destabilizing tracking.
In contrast, in the optical disk in accordance with the present invention, it is presumed that the width of the groove WG is substantially equal to the width of the land WL in the first width varying portion and the second width varying portion, both of which serve as an address region. Further, a first width portion is provided with a width smaller than the width of the groove WG and a second width portion is provided with a width greater than the width of the groove. This reduces asymmetry in the push-pull signals on the whole, effecting more stable tracking.
An optical disk in accordance with the present invention utilizes both a groove and a land as a recording track and includes:
first pit strings and second pit strings of pits lined along a length of a track, provided sequentially in first recording tracks which are either grooves or lands,
wherein:
letting inner and outer ends of the disk be designated as first and second sides respectively, or vice versa,
a first pit string forms a pair with another first pit string in a first recording track which is adjacent thereto on the first side with respect to a specific first pit string, so that the pair of first pit strings of an identical pit arrangement are provided within an identical angular range with respect to a center of the disk; and
a second pit string forms a pair with another second pit string in a first recording track adjacent thereto on the second side with respect to the second pit string following the specific first pit string, so that the pair of second pit strings of an identical pit arrangement are provided within an identical angular range with respect to the center of the disk.
In Laid-Open Patent Application 1, pits are located discretely on either one of the sides of a light beam spot moving over an address region in a recording track which is a land, which causes asymmetric push-pull signals to be produced. This undesirably destabilizes tracking.
In contrast, in the optical disk in accordance with the present invention, as a light beam spot moves over an address region in a recording track flanked by first recording tracks, the pit strings to the right and left of the light beam spot share an identical arrangement either in the first address region (the first pit string P1) or in the second address region (the second pit string P2). This arrangement effects more stable tracking compared with the preceding optical disk in which pits are located discretely.
An optical disk in accordance with the present invention utilizes both a groove and a land as a recording track and includes:
first width varying portions each having a track width which varies between a first width and a second width and second width varying portions each having a track width which varies between a first width and a second width, the first and second width varying portions being provided sequentially in first recording tracks which are either grooves or lands,
letting inner and outer ends of the disk be designated as first and second sides respectively, or vice versa,
a first width varying portion forms a pair with another first width varying portion in a first recording track which is adjacent thereto on the first side with respect to a specific first width varying portion, so that the pair of first width varying portions having an identical arrangement of the first and second widths are provided within an identical angular range with respect to a center of the disk;
a second width varying portion forms a pair with another second width varying portion in a first recording track adjacent thereto on the second side with respect to the second width varying portion following the specific first width varying portion, so that the pair of second width varying portions having an identical arrangement of the first and second widths are provided within an identical angular range with respect to the center of the disk; and
WG≈WL and W1 less than WG less than W2, where WG is a width of the groove, WL is a width of the land, W1 is the first width, and W2 is the second width.
In the optical disk in accordance with the present invention, a specific first width varying portion forms a pair with another first width varying portion which is adjacent thereto on the first side as described above, and the second width varying portion following a specific first width varying portion forms a pair with another second width varying portion which is adjacent thereto on the second side as described above. Therefore, as a light beam spot moves (scans) over a recording track flanked by first recording tracks, the light beam spot scans the first width varying portion and the second width varying portion on both sides of the recording track. This arrangement produces large and symmetric changes in the quantity of reflected light in a direction vertical to the length of a track, compared with an arrangement in which the first width varying portion and the second width varying portion are provided in every other groove. This further stabilizes tracking.
An optical disk in accordance with the present invention has a groove and a land,
wherein:
address information is stored in a string of pits lined along a length of a track, some of the pits being located relatively close to a center of the disk and the others relatively close to a circumference of the disk so that the pit string extends along the length of a track, but wobbles in a radial direction of the disk.
In the optical disk disclosed in Laid-Open Patent Application 2, address information is provided in the form of grooves that wobble right and left in address regions following grooves (G1 and G2). The wobbling of a groove is detected as changes in the quantity of reflected light or changes in push-pull signals. Since the groove wobbles right and left continuously, the changes in the quantity of reflected light and in push-pull signals are continuous, which increases reproduction jitter in the reproduction of address information and thereby increases errors in the detection of addresses.
In contrast, in the optical disk in accordance with the present invention, address information is provided in the form of a pit string that wobbles right and left in the address region. The wobbling of the groove is reproduced and detected. Since the wobbling pits are not provided continuously, the wobbling changes sharply at the edges of pits, which reduces reproduction jitter in the reproduction of address information and thereby decreases errors in the detection of addresses.
An optical disk in accordance with the present invention utilizes both a groove and a land as a recording track and includes:
a wobbling pit string constituted by:
an inner string of pits lined along a length of a track in an inner side of a central line of a track in a radial direction of the disk; and
an outer string of pits lined along a length of a track in an outer side of a central line of a track in a radial direction of the disk, the outer string being displaced off the inner string along a length of a track.
In the optical disk disclosed in Laid-Open Patent Application 2, information is provided in the form of grooves that wobble right and left following grooves (G1 and G2). The wobbling of a groove is detected as changes in the quantity of reflected light or changes in push-pull signals. Since the groove wobbles right and left continuously, the changes in the quantity of reflected light and in push-pull signals are continuous, which increases reproduction jitter in the reproduction of address information and thereby increases errors in the detection of addresses.
In contrast, in the optical disk in accordance with the present invention, information is provided in the form of a pit string that wobbles to the inner and outer sides of the central line of the track in a radial direction of the disk. The wobbling of the groove is reproduced and detected. Since the wobbling pits are not provided continuously, the wobbling changes sharply at the edges of pits, which reduces reproduction jitter in the reproduction of address information and thereby decreases errors in the detection of addresses.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.